Well, my kids are now teenagers, so it's more likely to be tunes from Minecraft-themed music videos these days. But when they were younger, I had a lot of Veggietales "Silly Songs" that got stuck there. When my son was a toddler, his favorite movie was "Milo and Otis", I cannot begin to tell you how many times I wound up humming, "Gonna take a walk outside today . . . ."
The Backyardigans...lots of cute kid songs that annoyingly get stuck in my head. Don't even want to think to hard about which songs in particular...one might get stuck in my head and I'll be doomed for the rest of the night. LOL